This invention regards a device for controlling the feeding of metal bars that have to be taken, through a proper guide equipment, to a multiple-spindle lathe.
In the aforesaid kind of lathes, unlike single-spindle lathes, succeding machining operations on workpieces are carried out, as it is known, by taking the workpieces sequentially to the tools or tool assemblies making up each working station. Therefore, in a multiple-spindle lathe the spindles are held by a fundamentally circular rotating drum, on which the spindles are at the same distance between one another, arranged angularly along a circumference.
These lathes are fed through appropriate guide equipment that is placed adjacent the lathe and consists basically of a series of tubular guides. The latter, too, are situated along a circumference, on the same longitudinal axis as the lathe spindles, and they are held by a turning frame that rotates synchronously with the spindle-holding drum.
The device that is the object of this invention is meant for the control of the feed of metal bars through the aforesaid guide equipment to the lathe, particularly into its spindles.
The brief description herein made of a multiple-spindle lathe and of guide equipment aims only at making this specification more complete and the features of this invention better understandable. In fact, the lathe and the guide equipment are not the object of this invention.
Finally, for a better comprehension of how the invention works, it is to be noted that the bar feed is not steady, but the bars jog and are fed according to the length required to make a new piece.
There are several devices for controlling the feed of bars to a multiple-spindle lathe as specified hereinbefore.
In a first type of these devices the bar-pushers to push bars into the guides are driven by only one drive motor, which turns a series of shafts, arranged on a drum substantially in a star-like manner, by means of a system of bevel gear pairs. The aforesaid drum rotates synchronously with the lathe drum. A pulley is splined to each shaft, and a steel-wire rope, to which a bar-pusher is fixed, is wound around this pulley. When the spindles stop the bars, there is the friction slip of the steel-wire ropes on the pulleys of the various shafts, since the bar cannot be fed any more. This leads to a high degree of wear concerning both the pulleys and the steel-wire ropes.
Another negative aspect of this device is that all ropes shall always be perfectly stretched in order to avoid sliding, which would prevent the bar from being fed, when the corresponding spindle is opened to allow the traverse of the former. That could bring about insufficient feeding, i.e. a length is fed that is less than that of the piece to be made, or even no feeding takes place. Therefore, besides the disadvantages first above described, the above mentioned device cannot be relied upon and requires steady maintenance, which implies that the lathe shall be inoperative for remarkable spans of time. That is extremely negative taking into account that the best output of a multiple-spindle lathe can be got only by minimizing its downtime.
Another known device is provided with a series of feed shafts arranged so as to resemble a star on a rotating drum. Each shaft is furnished with ts own motor reducer with clutch, which is operated whenever the corresponding bar has to be fed. This kind of device is extremely difficult to be built both because of the need of various drive motors and owing to the uneasy power supply of these motors applied to a turning drum. It goes without saying that the electric systems of these devices turn out to be complicated and prone to failures, which compel to stop the lathe, thus reducing its output rate as defined hereinbefore.
Both types of above mentioned devices are characterized also by the common disadvantage that they can be used only for one type of lathe, namely that where the spindle centre distance is the same as the centre distance of the bar feed controlling devices. It means that they cannot be used for a lathe where the spindle distance from the rotation centre of the drum is different from the distance of the pulleys or of the gears of the motor reducers from the rotation centre of their drum. This leads to the need of building a specific bar feed device for each lathe with a certain centre distance, as first above defined.
The disadvantages so far mentioned can be eliminated thanks to the subject of this invention, i.e. a device for controlling the feeding of metal bars to a multiple-spindle lathe.